The synthesis of polyether siloxanes by reacting chloropolysiloxanes with polyether diols requires an excess of polyether diols, measured by the molar ratio of OH groups to SiCl groups, in order to avoid the formation of A[BA].sub.x polymers or cross-linked polymers. In most cases, however, it is not possible to remove the excess polyether diol from the reaction mixture. Removal by distillation generally fails due to the high molecular weight of the polyether diol and the physical properties of the diol caused by this high molecular weight. Selective removal of polyether diol by washing is economically unfeasible and frequently not possible due to the surfactant properties of the polyether siloxane.
For the addition reaction between a polyether and an olefinic double bond, such as allyl polyether, and hydrogensiloxanes, it is also necessary to use an excess of polyether, since a portion of the polyether is not available for the addition reaction due to isomerization. The addition reaction proceeds quantitatively with respect to the SiH groups within an economically justifiable time only in the presence of excess amounts of polyether. The problem of removing the isomerized or excess unreacted amounts of allyl polyether also exists in such a procedure.